HTLV-I Tax induces the aberrant expression of various growth related cellular genes by activating the NFkappaB/Rel transcription factors. Recent studies demonstrate that Tax activation of NF-kappaB/Rel is associated with the proteolytic degradation of IkappaB-alpha and IkappaB- beta, two major cytoplasmic inhibitors of NF-kappaB. The overall objective of this proposal is to explore the biochemical mechanisms underlying Tax- induced phosphorylaiton and degradation of I,kappaB-alpha as well as the inactivation of IkappaB-beta. The specific aims are twofold; (i) to identify and functionally characterize IkappaB-alpha protein kinases; (ii) to explore the mechanism by which Tax induces the degradation of IkappaB- beta. The IkappaB-alpha specific protein kinases will be isolated by goth biochemical and genetic (yeast two hybrid system) approaches. The isolated candidate IkappaB-alpha kinases will be characterized by both in vitro kinase assays and in vivo functional analyses. In addition, the expression pattern of the kinases in HTLV-I-infected and normal T cells will be investigated by Northern analysis. To investigate how Tax induces the degradation of IkappaB-beta, phosphopeptide mapping coupled with site directed mutagenesis will be initially performed to determine whether phosphorylation is required for Tax-induced IkappaB-beta degradation. Additionally, progressive deletions will be introduced to 1kappaB-beta to completely define the sequences within IkappaB-beta that are involved in the Tax-mediated inactivation of this inhibitor. Together, these proposed experimental approaches should provide important insights into early steps of the development of ATL.